Electric power cable



Patented Sept. 25, 1945 UNITED STATES PATENT OFFICE ELECTRIC rowan CABLE John Krauss Webb, London, W. C. 2, England, assignor to International Standard Electric Corporation, New York, N. Y.

N Drawing. Application February 11, 1938, Se-

iiggll zNo. 190,053. In Great Britain March 19,

9 Claims. (01. 174-23) This invention relates to electric power cables e. g., oil from that part of the cable where it is and has for its object to provide improved bardesired to apply the polymerisable material, e. g., riers therein and improved methods of utilising styrene to complete the joint, termination or styrene or a similar polymerisable material in the plug, by dissolving out the oil in a suitable solvent application of joints, plugs or terminations in such as benzene. The solvent may be boiled 01f power cables of the impregnated type and the and replaced by monomeric styrene which is subgeneric expression barrier when employed in sequently polymerised in situ as described in the this specification is intended to include joints, aforesaid prior patents. plugs and terminations. The preferred method is to flush the insulation The present invention is particularly applicable 10 originally with benzene (Cal-Is) or other suitable to be ed in Co jun tion with the barriers disvolatile solvent. The solvent, held initially below Closed in U. te s 2,105,567; 1 its boiling point dissolves out considerable quanand 2,209,895 which cover the provision of styrene titles of oil and means are provided for drawing barriers in the form of joints, terminations and off the mixture of solvent and oil until substanplugs in electric power cables. tially pure solvent is passing through the cable When it is desired to make a styrene joint, plug, or barrier. The heating may then be increased, or termination in a cable system which has ins that temperatures in excess of the boiling Sulation Consisting f P p impregnated With Oil point of the solvent (which may be under reduced due regard must be p the fol w ng CO pressure due to the evacuation or suction at the Sidorotion. There is a t y for oil from h drawing-off point) are attained and the solvent cable insulation to seep into the barrier before is thus boiled off.

it is polymeriscd and contaminate. the styrene. Th lv t is th n replaced by monomeric At the interface of the barrier insulation and the t r 1, th abl r barrier is reimpregnated cable insulation the styrene and oil are of necesth monomeric styrene. Polymerisation is then sity mixed together so that there is no sudden effected, transition from oil to styrene with the result In order that th invention may be'clearly unthat after polymerisation (in conjunction with, filerstgod reference ill now be made in more 0 p fihloiinaiied diphenyl) e detail to the application of the present invention pregnated insulation is merged into the polyt t joints, plugs and terminations described styrene. This effect is advantageous both from so in t aforementioned patents, the electrical and mechanical points oi view, but t cable plugging process d scribed in U. 5. any excess o oil which finds its Way into the Patent No. 2,209,895 the oil resisting plug or terrier is detrimental. For example, excess of oil, mina'bign was provided by introducing a polyresults in a very much inc eas d me Of p y-' merisable material, for example styrene, into merisation which is inconvenient. It also results as th ble insulation by means of tappings or in the mp p d being plastic so openings in the metal sheath and thereafter polythat the hydra resistance 0f the barrier is merising the material to form a plug in the cable. impaired- A difficulty which has now become apparent is So e amelioration ay be obtained sthat in the course of the replacement of the 011 ing the cable sheath in the vicinity of the barrier 40 with the styrene the latter t d t l ri and/or by freezing the cable on either side 01 with the result t the nipples may become the joint with cmbon dioxide (CO2) snowchoked with polystyrene before sufficient oil has The present invention aims to overcome this been replaced difliculty in the application of a polymerisable The above diff lt may be overcome in material Such as styrene to impregnated cablescorclance with the present invention by first of all on impregnated cables caused by the news feeding a suitable solvent into the cable instead sity for replacing the Original impregnam in of feeding in styrene. In this manner the oil at cable by the polymerisable material- This that part of the cable at which the plug is to be rial belongs a class which may be generally formed is replaced by the solvent (e. g., benzene scribed as readily polymerizable aromatic hydro- CQHG); thereafter the Solvent may be boiled carbons of the Vinyl type for which the general and monomeric styrene fed into the cable. In mimomeric formula may be set down as follows: addition to the adjustment of the oil content, the

R following advantages are obtained: I (A, 1. A saving in monomeric styrene (which 15 Hzzcg a more expensive than benzene) since n; styrene R is an aromatic hydrocarbon radical contaminated with oil need be drawn 0 33%;: contains i ess than four benzene rings and 2. Polymerisation of the styrene during oil dls= N is the number of vinyl groups attached to the placement is avoided with a resultant gain of eificiency in the process. In addition to the advantages specified above in the process of formaromatic radical. Briefly stated, the invention big oil resisting plugs or terminations in oil impregnated cables, the present invention also renders possible a simplification in the preparation of a cable joint. The joint described in my Patent No. 2,105,567 involves the use of paper tapes impregnated with monostyrene which comprises the added insulation. Difiiculties are experienced in connection with the storing and transportation or paper tapes impregnatedwith monomeric styrene, because unless they are pre-polymerised there is a tendency for partial polymerisation to take place during storage or transpor-' tation and unless the papers are kept at a low methods by means of which styrene joints may be produced and the above dimculties overcome. One method is to use ordinary oil impregnated tapes in making the joint and thereafter to replace the oil with styrene in the manner described above in connection with U. S. Patent No. 2,209,895. It is therefore now possible to use ordinary oil-impregnated paper or papers impregnated with any desired compound, e. g., resin oil, chlorinated diphenyl, chlorinated naphthalene or preferably methyl abietate known under the trade name Abalyn. The characteristics of the compoundshould be chosen to ensure minimum absorption of moisture during storage, transport and application to the joint, to provide suitable lubricatibn'for the taping process and to ensure sufilcient solution in the solvent such as benzene.

After the manual construction of the Joint and the fitting and plumbing of the sleeve, two nipples are fitted into the cable sheath (exterior to the plumbs of the sleeve). A nipple may also be inserted midway between these two nipples, i. e., at the centre or the joint sleeve. The technique is then similar to that for m a styrene plug in a cable.

an advantage of the present process is that the added insulation is firmly bonded to the cable insulation and the use of oil impregnated paper tapes is simplified.

The present invention may also be applied to the preparation of cable terminations as described in U. 8. Patent 2,209,894. by feeding solvent into the cable end prior to the application 7 of the polymerisable material thereto.

The provision of polymerised barriers in single core cables is a relatively simple matter since the oil solvent used to dissolve out the oil may readily be constrained to flow along the cable strand and through the dielectric, thus dissolving,

ful in dealing with belted cables. The cable is treatedin a similar manner to a single core cable, 1. e., solvent is passed through in an attempt to replace the oil. It will soon be found that after some oil has been ejected, the solvent will come through clear, evidently due to the easy path ofiered by the now oil-tree spaces. It now, however, the solvent is drawn oil? by the application of heat and vacuum, the oil which normally cannot be reached in the strands and core papers will dlfiuse towards the dry worming spaces under the combined influence of the forces due to gravity and capillary attraction. A further flushing of solvent will then remove this oil and the process may be repeated until suificient is removed to permit of re-impregnation with styrene, which will then penetrate suificiently to form an effective barrier upon polymerisation. The above method may if desired be used in connection with H-type cables (1. e., screened cores) but the difiusion'of oil would in such an application of the method take rather longer than in the case of belted cables.

When applying the solvent to the cable insulation, nipples may be inserted into the cable sheath at each side of the barrier so that the solvent may be passed through the insulation from one end of the barrier to the other to dissolve out the impre nant and then after removal of the solvent an impregnant styrene or other suitable polymerisable material may be fed into the insulation. Alternatively and especially in the provision of a joint a sleeve maybe provided, around the insulation having an orifice to permit the insertion of a nipple or nipples adjacent to the centre of the joint so that the solvent may be passed through the insulation from the centre to each end of the barrier.

In order to assist in driving ofi the solvent and dissolved impregnant and in polymerising the material to form the'barrier a heating coil or coils may be provided to surround the cable sheath (e. g., in the case of a plug or termination) or a sleeve surrounding the insulation to. g.,

in the case of a joint) at the position at which the barrier is to be formed. Alternatively the cable sheath or the sleeve may be directly heated by the passage therethrough of an electric current of sumciently high amperage.

In multi-core cables it may be found advantageous to form the barrier in stages; for example in the case of a belted cable the impre nant in the core insulation and the worming spaces may be removed by repeated applications of solvent as described above, thereafter polymerisable material may be fed into the insulation and polymerised. Having formed a barrier in the core insulation and in the worming spaces as described the impregnant may be removed from the belt insulation bythe application of solvent and polymerisable material may thereafter he applied thereto. In carrying out the above process the belt insulation may be removed for the length of the barrier, the first stage may then be completed and the belt insulation replaced or alternatively the belt insulation may be built up by the application of impregnated papers thereto which may then be treated for the removal of impregnant and the application of polymerisable material thereto.

The application of solvent and the removal of solvent and dissolved impregnant may be iacilitated by introducing the solvent from a suitable bomb held under pressure and by applying a partial vacuum to the outlet nipple or nipples.

' dissolve out a substantial at thatpart of the cable, allowing the solvent 2,ss5,55a

What is claimed is: 1. A method of preparing a liquid resisting barrier in an impregnated cable which comprises cooling the portions of'the cable adjacent the part thereof in'which said barrier is to be formed flowing out of the ihsulation, heating the cable to drive off the remainder of the solvent, introcores, thereafter repeating the treatment with solvent until the solvent removed from the said cable is substantially pure, heating said cable'to drive off the remainder of the solvent, introducing a polymerlzable material into the insulating material in the spaces and around the cores from which the impregnant has been removed and thereafter polymerizing the material to form a ducing' a polymerizable material into that part of the cable from which the impregnant has been substantially removed, and thereafter polymerizing the material to form a barrier in the cable.

solid barrier in the cable.

5. A method according to claim 4 in which a nipple is provided at each side of said barrier characterized in that the solvent is introduced through a nipple disposed atone side of the bar rier and is drawn off through the nipple at the other side of the barrier.

6. A methodaccording'to claim 4 characterized in that the solvent is introduced centrally of the barrier and is drawn off at each side of the barrier.

2 A method of providing a solid Joint in an impregnated cable which comprisesvbuilding up the insulation around the Joint with fibrous material impregnated with a suitable compound, disposing a protective sleeve around the insulation at the joint, cooling a portion of said cable adiacent the ends of said protective sleeve to render the impregnant of said cable substantially immobile, feeding a volatile solvent into said built-up insulation and causing it to flow there-'- through to dissolve out a substantial part of the impregnant, allowing the solvent and dissolved impregnant to flow out of said Joint, continuing feeding solvent into the insulation until substantially puresolvent is' flowing out of said insulation, heating the Joint to drive oil. the remainder of the solvent, introducing a polymerizable material into the built-up insulation and thereafter polymerizing said'material to form a solid Joint in the cable) 3. A method of providing a solid termination in an impregnated cable which comprises cooling theportionsof the cable adjacent the part thereof in which said barrier is to be formed to render the impregnant of the cable substantially immobile, feeding a volatile solvent into the cable insulation adjacent tothe end of the cable to part of the impresnant and dissolved impregnant to flow out of the cable, continuing feeding solvent into the insulation until substantially pure solvent, is flowing out of the insulation, heating the cable to drive off the remainder of the solvent introducing a polymerizable material into that part of the cable from which the impregnant has been substantially removed and thereafter polymerizing the material to form a solid termination in the cable.

4. A method of providing a barrier in an impregnated multi-core cable which comprhes cooling the portions of the cable adjacent the part thereof in which said barrier is to be formed to render the impregnant of the cable substantially immobile, feeding a volatile solvent into the cable to dissolve out nant from the fibrous vent and dissolved impreg'n'ant from said cable, allowing impregnant th corestodiifuseintothespacebetweenthe 7. A method of preparing a liquid resisting barrier in an impregnated cable which comprises cooling the portions of the cable adjacent the part thereof in which said barrier is to be formed to render the impregnant of the cable substantially immobile, feeding a solvent into the cable and causing said solvent to flow through that part of th cable insulation in which the barrier is to be formed to dissolve out a substantial part of the impregnant therefrom, allowing the solvent and dissolved impregnant to flow out of the cable, continuing feeding in solvent into the insulation until substantially pure solvent is flowing out of the insulation, introducing a polymerizable material into that part of the cable from which the impregnant has been substantially removed, and thereafter polymerizing the material to form a barrier in the cable.

8. A fluid stop occupying a predetermined limited length intermediate the end sections of a finished, substantially intact, sheathed, multiconductor cable having conductors initially insulated with laminated material impregnated with insulating fluid and having filler strips in the channels between conductor insulation, comprising a solid polymer formed in situ from a monomer having the general formula rier, feeding a volatile solvent into the cable to a substantial part of the impregnant dissolve out I from the ilbrous insulated materials in the spaces between cable cores, removing the solvent and dissolved lmpregnant from the cable, then after a period for diffusion of core impregnant into spaces between cores,'repeating said feeding and a substantial part or the imam.- insulating materials in the spaces between the cable cores, removing the sol-' n from the insulation around 7 removing operations until the solvent removed,

fromsaid cable is substantially pure. driving 0! the remainder of the solvent by heat application,

introducing a poiymerisable material into the in- 'sulating material in the core spaces and around the cores from which the impregnant has been removed, then polymerizing'thematerial and then' repeating said barrier-forming operation respect-z .ing the belt lnliilltion.

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